Lithium compound containing electric cells and batteries containing such cells are modern means for storing energy. They exceed conventional secondary batteries with respect to capacity and life-time and, in many times, use of toxic materials such as lead can be avoided. However, in contrast to conventional lead-based secondary batteries, various technical problems have not yet been solved.
Secondary batteries based on cathodes based on lithiated metal oxides such as LiCoO2, LiMn2O4, and LiFePO4 are well established, see, e.g., EP 1 296 391A1 and U.S. Pat. No. 6,962,666 and the patent literature cited therein. Although the batteries mentioned therein exhibit advantageous features, they are limited in capacity. For that reason, numerous attempts have been made to improve the electrode materials. Particularly promising are so-called lithium sulfur batteries. In such batteries, lithium will be oxidized and converted to lithium sulfides such as Li2S8−a, a being a number in the range from zero to 7. During recharging, lithium and sulfur will be regenerated. Such secondary cells have the advantage of a high capacity.
A particular problem with lithium sulfur batteries is the thermal runaway which can be observed at elevated temperatures between, e.g., 150 to 230° C. and which leads to complete destruction of the battery. Various methods have been suggested to prevent such thermal runaway such as coating the electrodes with polymers. However, those methods usually lead to a dramatic reduction in capacity. The loss in capacity has been ascribed—amongst others—to formation of Lithium dendrites during recharging, loss of sulfur due formation of soluble lithium sulfides such as Li2S3, Li2S4 or Li2S6, polysulfide shuttle, change of volume during charging or discharging and others.
In WO 2008/070059 various materials are disclosed for coating electrodes for lithium sulfur batteries. However, the thermal runaway problem has not been solved satisfactorily.